From the discovery of superconductivity in 1911 to the recent past, essentially all known superconducting materials were elemental metals (e.g., Hg, the first known superconductor) or metal alloys (e.g., Nb.sub.3 Ge, probably the material with the highest transition temperature T.sub.c known prior to 1986).
Recently, superconductivity was discovered in a new class of materials, namely, metal oxides. See J. G. Bednorz and K. A. Muller, Zeitschr. f. Physik B-Condensed Matter, Vol. 64, 189 (1986), which reports superconductivity in lanthanum barium copper oxide.
The latter report stimulated worldwide research activity, which very quickly resulted in further significant progress. The progress has resulted, inter alia, to date in the discovery that compositions in the Y--Ba--Cu--O system can have superconductive transition temperatures T.sub.c above 77 K., the boiling temperature of liquid N.sub.2 (see, for instance, M. K. Wu et al, Physical Review Letters, Vol. 58, Mar. 2, 1987, page 908; and P. H. Hor et al, ibid, page 911). Furthermore, it has resulted in the identification of the material phase that is responsible for the observed high temperature superconductivity, and in the discovery of composition and processing techniques that result in the formation of bulk samples of material that can be substantially single phase material and can have T.sub.c above 90 K. (see the U.S. patent application Ser. No. 024,046, entitled "Devices and Systems Based on Novel Superconducting Material," filed by B. J. Batlogg, R. J. Cava and R. B. van Dover on Mar. 10, 1987, co-assigned with this and incorporated herein by reference, which is a continuation-in-pan of an application filed by the same applicants on Mar. 3, 1987, which in turn is a continuation-in-part of application Ser. No. 001,682, filed by the same applicants on Jan. 9, 1987). See also R. J. Cava et al, Physical Review Letters, Vol. 58(16) pp. 1676-1679 (1987).
The excitement in the scientific and technical community that was created by the recent advances in superconductivity is at least in part due to the potentially immense technological impact of the availability of materials that are superconducting at temperatures that do not require refrigeration with expensive liquid He. Liquid nitrogen is generally considered to be perhaps the most advantageous cryogenic refrigerant, and attainment of superconductivity at liquid nitrogen temperature was a long-sought goal which until very recently appeared almost unreachable.
Although this goal has now been attained, there still exist barriers that have to be overcome before the new oxidic high T.sub.c superconductive materials can be utilized in many technological applications. In particular, techniques for forming high T.sub.c superconductive bodies of technologically significant shape have to be developed. Among the shapes of technological significance are thin layers, frequently patterned, on a non-superconducting substrate.
Prior art metallic superconductors have been prepared in thin layer form by such techniques as vapor deposition and sputtering. Such thin films have found use, for instance, in Josephson junctions and in various detectors.
For a general overview of some potential applications of superconductors see, for instance, B. B. Schwartz and S. Foner, editors, Superconductor Applications: SQUIDS and MACHINES, Plenum Press 1977; and S. Foner and B. B. Schwartz, editors, Superconductor Material Science, Metallurgy, Fabrications, and Applications, Plenum Press 1981. Among the applications are power transmission lines, rotating machinery, and superconductive magnets for e.g., fusion generators, MHD generators, particle accelerators, levitated vehicles, magnetic separation, and energy storage, as well as junction devices and detectors. It is expected that many of the above and other applications of superconductivity would materially benefit if high T.sub.c superconductive material could be used instead of the previously considered relatively low T.sub.c materials.
In particular, the existence of a method for producing thin layers of high T.sub.c superconductive oxide material would likely result in considerable economic benefit. For instance, such a method could be used to produce junction devices and detectors that are operable at higher temperatures than prior art devices, and could perhaps be employed in novel ways, e.g., to interconnect electronic circuits or chips. In particular, a method that can be used to produce superconductive oxide thin films economically and conveniently, without the use of expensive equipment such as vacuum chambers, would be of obvious benefit. Such a method is disclosed below.